Filament networks and methods of making same for use in the manufacture of products with enhanced characteristics

ABSTRACT

The present invention relates to the production of filament networks that can serve as intermediates for the production of goods to impart enhanced performance characteristics such as strength and flame resistance. This filament network intermediate includes a plurality of filaments of one or more types of materials, wherein the filaments are randomly associated in the network in a wool-like configuration. The present invention also relates to a two-step process for making filament networks that may be performed by a single apparatus. The present invention further relates to an apparatus for feeding and drafting fibers to produce filament networks.

TECHNICAL FIELD

The present invention relates to the production of filament networks that can serve as intermediates for the production of goods to impart enhanced performance characteristics such as strength and flame resistance. This filament network intermediate includes a plurality of filaments of one or more types of materials, wherein the filaments are randomly associated in the network in a wool-like configuration. The present invention also relates to a two-step process for making filament networks that may be performed by a single apparatus. The present invention further relates to an apparatus for feeding and drafting fibers to produce filament networks.

BACKGROUND OF THE INVENTION

Carbon fibers are long bundles of linked graphite plates that form a crystal structure laying parallel to the axis of the fiber. Like all crystalline structures, they are anisotropic. Their elastic modulus is higher in the direction of the axis than it is against the axis. In other words, the individual filaments in the fibers can withstand pulling from one end of the fiber to the other to a greater degree than they can withstand bending at an angle from the axis. Accordingly, most carbon fibers are assembled from thousands of individual filaments.

Carbon fibers exhibit remarkable mechanical, physical and chemical properties. In addition to being nonflammable, they are light, stiff, and strong. Their strength can compete with the strongest steels and their stiffness is generally greater than any metal, ceramic or polymer-based material. Furthermore, carbon fibers provide additional desired properties, including excellent corrosion and fatigue resistance, and dimensional stability. Thus, carbon fibers and their composites with other materials are ideally suited to applications where chemical inertness, strength, stiffness, lightness, and fatigue resistance are important requirements. For example, in the aerospace and defense industries, carbon fibers have been increasingly used both in the interior of aircrafts as flame resistant materials as well as in the critical structural components to increase fuel efficiency and to enhance structural strength.

Carbon fibers are made from a large variety of precursor materials. Among these precursors are polyacrylonitrile (PAN), cellulosic fibers such as rayon and cotton, petroleum or coal tar pitch, and certain phenolic fibers. However, different precursor materials produce carbon fibers with different morphologies and different specific characteristics. Pitch-based carbon fiber has much greater stiffness, but it is brittle and costly to produce. Even so, it is widely used in high-performance applications, such as military aircraft, spacecraft, and missiles. In contrast, PAN-based carbon fibers have much greater tensile strength and are relatively low in cost. Accordingly, this precursor material is particularly well suited for use in the construction of consumer goods, such as sporting goods and high-performance apparel.

Various methods for the production of carbon fibers are known, and include pyrolytic processes, or “pyrolysis” reactions. It is well established that the mechanical properties of carbon fibers are improved by increasing crystallinity and orientation. The best way to achieve this is to start with a highly oriented precursor and then maintain the initial high orientation during the process of stabilization and carbonization through tension. Thus, one common pyrolysis reaction is an “oxidative stabilization” process in which a fiber is treated at about 200-300° C. under tension in an oxidizing environment. During the process, oxygen, nitrogen and/or hydrogen is removed from the fiber, resulting in an increase of carbon content in the fiber. In addition to preventing fiber shrinkage, the tension applied during this process maintains the molecular orientation of the fiber, which in turn increases the tensile strength of the stabilized fiber.

Polyacrylonitrile (PAN) is one of the most common precursors for carbon fibers because of the combination of tensile and compressive properties as well as the carbon yield. During pyrolysis, the oxidation and stabilization induce intramolecular cyclization of the oriented molecules with the release of most of the hydrogen and part of the nitrogen from the fibers. The resulting PAN polymers are called “oxidized PAN”, which have a carbon content of about 55-68% and a density of about 1.30 to 1.50 g/cm³. As flame resistant materials, oxidized PAN fibers have several advantages. For example, these fibers have high Limiting Oxygen Indexes (“LOI”), typically between 40-60% oxygen, making them much more flame resistant than many other organic fibers. In addition, they have excellent heat insulation properties, which are derived from the heat stabilized PAN chemistry and resultant low thermal conductivity. Also, unlike other flame resistant organic fibers, oxidized PAN fibers retain their appearance, hand and textile characteristics after open flame exposure. Furthermore, the oxidized fibers are electrically non-conductive and function as effective electrical insulator even after exposure to heat and open flames. They also have excellent chemical resistance to organic solvents and most acids and bases. Lastly, oxidized PAN fibers are much softer and more pliable than carbon fibers. Accordingly, oxidized PAN fibers are ideally suited for heat resistant, thermal insulation and textiles for high-technology applications, and have been used as fire blocking fabrics for seating in aerospace and automobile industries, and as protective clothing for people exposed to the danger of an open flame.

Currently, there are three types of oxidized PAN fibers available commercially: staple fibers, large tow fibers and small tow fibers. In order to use these fibers in the production of industrial and consumer products, they are often spun into yam using complex, multi-step processes. For staple fibers, the first step in the production of yarn is “carding”, in which the fibers are opened and combed over cylinders that contain extremely fine wires or teeth aligned, and then aligned in one direction to form a large loosely assembled but not twisted continuous strands of fibers known as “sliver”. Second, several strands of sliver are then drawn multiple times onto drawing frames to further align the fibers to improve uniformity as well as to reduce the diameter of the sliver. Third, the drawn sliver is fed into a roving frame to produce “roving” by further reducing the diameter and imparting a slight false twist. Finally, the roving is fed into the spinning (i.e., winding and/or twisting) frame where it is spun into yarn. For large tow, the first step is different, and consists of a stretch-breaking process in which the large tow is broken into multiple fragments and aligned into sliver. The sliver is then further processed as described above. These processes are laborious, inefficient and costly, and often require more than one type of apparatus to perform.

Accordingly, there is a need to develop processes that are efficient and economical that can ideally be performed by a single apparatus using less complex operational manipulations. There is also a need to produce intermediates for use in both woven and nonwoven goods. Hence, the present invention relates to the production of fine “filament networks” that can serve as intermediates for the production of goods to impart enhanced performance characteristics such as strength and flame resistance. The present invention also relates to a process for making filament networks in two simple steps that are performed by a single apparatus. The present invention further relates an apparatus for feeding and drafting fiber to produce filament networks.

SUMMARY OF THE INVENTION

In accordance with the present invention, a filament network intermediate includes a plurality of wool-like filaments with a length of no greater than 40 cm. The filament network is obtained from a variety of fibers, including oxidized PAN fibers, stainless steel fibers, aramid fibers, and polyester fibers. Unlike their precursor fibers, which generally have long and well aligned filaments, the filament networks produced are wool-like filament networks which contain a plurality of short wavy filaments randomly piled together and the filaments are held together by mechanical, physical and noncovalent chemical forces. In one aspect, oxidized PAN filament networks are produced from long and aligned oxidized PAN fibers. The filaments of the networks have a length of no greater than 22 cm and a width of no greater than about 12 micrometers. In another aspect, a stainless steel filament network is produced from an aligned and long stainless steel fiber. The filaments of the network product have a length of no greater than about 10 cm and a width of no greater than about 8 micrometers. In yet another aspect, the aramid filament network is produced from an aligned and long aramid fiber. The filaments of the network product have a length of no greater than about 22 cm and a width of no greater than about 12 micrometers.

In another embodiment of the present invention, an apparatus for producing a filament network includes a feeding component and a drafting component. The feeding component delivers one or more types of fibers to the drafting component. In one aspect, the drafting component comprises two pairs of rollers and a pressurizing element, such as a weight element. The weight element can be adjusted to exert appropriate pressure on each pair of rollers so that the fiber can only be moved by the rotation of the rollers. The drafting of a fiber is accomplished by the force created by the two pairs of rollers, wherein the first rollers rotate slower than the last rollers. This causes the fiber to be both stretched and broken between the two pairs of rollers. In another aspect, the drafting component further comprises one or more intermediate pairs of rollers. The intermediate pairs are so arranged that the fiber to be drafted contacts first with the first rollers, then with the intermediate rollers, and then with the last rollers to exit the drafting component to form a wool-like filament network. Preferably, the apparatus comprises one intermediate pair of rollers. In yet another aspect, the apparatus of the present invention may further comprise a twisting and winding component, wherein the filament network formed during the feeding and drafting components is spun into yarn.

In yet another embodiment of the present invention, a method of forming a fluffy and randomized filament network intermediate product from an aligned and long fiber includes feeding and drafting steps. One or more types of fibers are first delivered simultaneously from the feeding component to the drafting component with minimum twisting. The fibers are then drafted to produce the filament network intermediate. This intermediate can be further processed into fine spun yarns on the same apparatus, or it can be used in the manufacture of nonwoven products.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the structures of PAN, oxidized PAN, and PAN carbon fiber.

FIG. 2 depicts an exemplary apparatus.

FIG. 3 depicts an expanded view of the drafting component of the apparatus of FIG. 2.

FIG. 4 depicts a graphic representation of the drafting, and twisting and winding components of the apparatus of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the production of filament networks that can serve as intermediates for the production of goods to impart enhanced performance characteristics such as strength and flame resistance. This filament network intermediate includes a plurality of filaments of one or more types of materials, wherein the filaments are randomly associated in the network in a wool-like configuration. The present invention also relates to a two-step process for making filament networks that may be performed by a single apparatus. The present invention further relates to an apparatus for feeding and drafting fibers to produce filament networks.

To facilitate understanding of the invention set forth in the disclosure that follows, a number of terms are defined below.

DEFINITIONS

The term “filament” refers to a single strand of fibrous material, which may be part of an organized or random collection of filaments. For example, a plurality of filaments may be brought together by winding and/or twisting the filaments together to form yarn.

The term “yarn” refers to an assemblage of twisted filaments with a virtually continuous length that is suitable for use in weaving, either alone or with other filaments or yarns, into textile materials.

The term “filament network” refers to a random collection of untwisted filaments that are held together by mechanical, physical and noncovalent chemical forces.

The term “wool-like” refers to a filament network in which the random collection of untwisted filaments includes individual filaments that are partially or completely crinkled, curled, crimped, wavy and/or otherwise curved.

The term “PAN” refers polyacrylonitrile, as depicted in FIG. 1.

The term “oxidized PAN” refers to polyacrylonitrile fiber which has been oxidatively stabilized, as depicted in FIG. 1. Oxidized PAN can also be further processed to form carbonized PAN as also depicted in FIG. 1.

The term “carbon fiber” refers to a fiber containing at least 90% carbon, which is usually obtained by the controlled pyrolysis of appropriate fibers.

The term “tow” refers to a collection of untwisted fibers that are arranged longitudinally, which is often referred to in terms of the number of filaments in the collection, such as 3K, 6K, etc.

The term “LOI” refers to the limiting oxygen index, which is a measure of the percentage of oxygen that has to be present to support combustion of a material. The higher the LOI, the lower the flammability.

The term “draft ratio” refers to the ratio of the speed of the first and last rollers of a drafting component.

The meaning of other terminology used herein should be easily understood by someone of reasonable skill in the art.

Starting Materials

The present invention provides a simple, efficient and cost-effective method to draft various fibers into wool-like filament networks. A typical fibrous starting material has straight, long filaments with very limited inter- and intra-filament twisting. The filaments are also well organized and aligned longitudinally (i.e., they are parallel to one another.) An exemplary starting material includes, without limitation, PAN fibers, oxidized PAN fibers, polyester fibers, aramid fibers, nylon fibers, rayon fibers, and metal fibers such as stainless steel fibers, nickel fibers, alloy fibers.

Typical starting or precursor materials are filament tows consisting of parallel filaments of a uniform length equal to the length of the tow. Preferably, these precursor tows have a twist number less than 50 per meter and each filament has a length of no less than 2 meters. More preferably, the precursors have a twist number less than 25 per meter. Yet more preferably, the precursors have a twist number less than 10 per meter. Most preferably, the precursors have a twist number less than 5 per meter. For polymeric fibers, it is preferred that each filament has a decitex (1 g/10,000 meters) of no greater than 67 and the total measure of the tow is no greater than 32,000 decitex. For stainless fiber, it is preferred that each filament has a decitex of no greater than 550 and the total measure of the tow is no more than 260,000 decitex.

In one embodiment, the starting material is oxidized PAN tow with no greater than 192 K filaments and a filament diameter of no greater than 50 micrometers. Preferably, the oxidized PAN has a tow of no greater than 96K, and a filament diameter of no greater than 25 micrometers. More preferably, the oxidized PAN has a tow of no greater than 48K. Yet more preferably, the oxidized PAN has a tow of no greater than 24K. Yet more preferably, the oxidized PAN has a tow of no greater than 12K. Oxidized PAN tow is commercially available from a number of different companies, such as Asahi Chemical Industry Co., Ltd. at Osaka, Japan (LASTAN®), Zoltek at St. Louis, Mo. (PYRON®), SGL Carbon AG at Wiesbaden, Germany (PANOX®), Dow Chemical Company at Midland, Mich. (CURLON®), etc. However, the present invention is not limited by the source of oxidized PAN tow. In addition, many publications are available with sufficient information to allow one to manufacture oxidized PAN tow with desired structures and properties.

The present invention is also not limited by the chemical composition of oxidized PAN, which is a function of the composition of the PAN precursor, and the oxidative stabilization process to convert PAN into oxidized PAN. The PAN precursor can be, for example, a homopolymer of acrylonitrile, acrylonitrile based copolymers, and acrylonitrile based terpolymers. The copolymers preferably contain at least about 85% (by mole) of acrylonitrile monomers and up to 15% (by mole) of one or more mono-vinyl units. Exemplary other vinyl monomers that are able to copolymerized with acrylonitrile include methacrylic acid esters and acrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, methyl acrylate and ethyl acrylate; vinyl esters such as vinyl acetate and vinyl propionate; acrylic acid, methacrylic acid, maleic acid, itaconic acid and salts thereof; vinylsulfonic acid and the salt thereof.

The oxidized PAN that is useful in the practice of the present invention can be produced from various PAN fibers using well established oxidative pyrolytic processes. Normally, oxidative stabilization is performed at atmospheric pressure in the presence of oxygen at a temperature of about 200-300° C. The chemical composition of oxidized PAN is affected by the duration of time and the temperature of the oxidation process. In one aspect, the oxidized PAN used in the practice of the present invention has a density of about 1.30 to 1.50 g/cm³, a carbon content of about 55 to 68%, and an “LOI” (Limiting Oxygen Index) value of about 40 to 60%.

In another embodiment, the starting material is polyester fiber with a tow of no greater than 192K and a filament diameter of no greater than 50 micrometers. Preferably, the polyester fiber has a tow of no greater than 96K and the filament has a diameter of no greater than 25 micrometers. More preferably, the polyester fiber has a tow of no greater than 48K. Yet more preferably, the polyester fiber has a tow of no greater than 24K. Yet more preferably, the polyester fiber has a tow of no greater than 12K.

In yet another embodiment, the starting material is stainless steel fiber with a tow of no greater than 192K and a filament diameter of no greater than 50 micrometers. Preferably, the precursor fiber has a tow of about no greater than 96K and the filament has a diameter of no greater than 20 micrometers. More preferably, the stainless steel fiber has a tow of no greater than 48K. Yet more preferably, the stainless steel fiber has a tow of no greater than 24K. Yet more preferably, the stainless steel fiber has a tow of no greater than 12K.

In yet another embodiment, the starting material is an aramid fiber with a tow of no greater than 192K and a filament diameter of no greater than 50 micrometers. Preferably, the precursor fiber has a tow of no greater than 96K and its filament has a diameter of no greater than 20 micrometers. More preferably, the aramid fiber has a tow of no greater than 48K. Yet more preferably, the aramid fiber has a tow of no greater than 24K. Yet more preferably, the aramid fiber has a tow of no greater than 12K. An aramid fiber is an aromatic polyamide and comes with many different grades and properties for various applications. The aramid fiber has excellent environmental and thermal stability, static and dynamic fatigue resistance, and impact resistance. The fiber has the highest specific tensile strength of any commercially available continuous filament tow. Examples of aramid fibers include, but are not limited to, KEVLAR® by DuPont (Greenville, Del.), TWARON® and TECHNORA® by Teijin (Arnhem, Netherlands).

The methods and apparatuses of the present invention can also be used to draft two or more strands of fibers simultaneously. When the fibers drafted are of different types, a blended filament network is obtained. Other fibers that may be used include linear fibers that may be selected from natural or synthetic fibers. Exemplary fibers include carbon fibers, ceramic fibers, glass fibers, metal fibers, carbonaceous fibers (e.g. cotton, wool, polyester, polyolefin, nylon, rayon or novoloid phenolic), inorganic fibers (e.g. silica, silica alumina, potassium titanate, silicon carbide, silicon nitride, boron nitride, and boron), acrylic fibers, tetrafluoroethylene fibers, polyamide fibers, vinyl fibers, protein fibers, and oxide fibers derived from boron, thoria or zirconia.

Processing/Apparatus

In one aspect of the present invention, the apparatus of the present invention comprises feeding and drafting components, and an optional spinning component. The feeding process involves feeding a continuous precursor fiber into the drafting mechanism. The feeding process is passive and maintains the fiber in a flat configuration, with minimum twist (i.e. no more than double the twist of the starting material.)

Typically, the feeding component is a “ring spinning frame”. However, other conventional feeding methods may also be appropriate. Furthermore, the feeding component may comprise two or more feeding elements so that two or more strands of fibers may be drafted simultaneously. When the fibers fed are of different types, a blended filament network is produced.

FIG. 2 depicts a representative apparatus having a feeding component, a drafting component and a spinning component. As shown, the apparatus is a dual-mode apparatus that is capable of forming two yarns. The feeding component consists of four rollers, 1 a, 1 b, 2 a and 2 b, on which the starting material is placed. As discussed above, the starting material on rollers 1 a and 1 b, and 2 a and 2 b, may be the same or different.

The starting material enters the drafting component, and is fed through a system of roller pairs, 3 (first pair), 4 (second pair) and 5 (third pair), with the roller pairs being “pressurized” by application of pressure via pendulum 6. A more detailed depiction of the drafting component is shown in FIG. 3. It should be well understood that an alternative embodiment of this drafting component may consist of only two pairs of rollers. Alternatively, it is possible to include more than one feeding component in an apparatus, each with at least two pairs of rollers.

The drafting process produces a stretched fiber that exits the drafting component as a wool-like filament network. For the drafting process to be operated effectively, the rollers of each pair are arranged such that the center of each roller, i.e., the axis (shown as the “X” in FIG. 3), is parallel to each other. This parallel alignment is also depicted in FIG. 4 by the dashed line between rollers. Optionally, the axes of each pair may also be parallel to each other as depicted by the dotted line between the rollers of pair 4.

During the drafting process, each roller of a pair applies an equal and opposite pressure onto opposing sides of the fiber to a degree so that the fiber can only be moved by the rotation of the rollers and can not slip away from the rollers. The pressure applied onto each pair of rollers may be accomplished by any conventional method either independently or cooperatively. For example, a weight element can be used to exert appropriate pressure onto the rollers. The pressure can be generated by applying the weight element onto at least one of the rollers of each pair. To simplify the design of the apparatus of the present invention, the weight element is applied to only one of the two rollers of each pair.

Preferably, the drafting component has a single weight element 6 (a pendulum carrier) that cooperatively exerts appropriate pressure onto each pair of rollers so that the fiber can only be moved by the rotation of the mechanically driven rollers. Preferably, as shown in FIG. 2, one roller from the first 3 and second 4 pairs of rollers is attached to the pendulum carrier. The remaining two rollers 5 are preferably attached to the frame of the apparatus. The pressure is adjusted by the weight of pendulum and by varying the relative position of the pendulum carrier and the rollers. The pendulum carrier is preferably detachable from the drafting component or swings open on a hinge for easy access to the rollers. Rotation of the rollers may be accomplished by any conventional method manually or automatically.

The roller can be made from a variety of materials, including but without limitation, rubber, metals such as steel and aluminum, wood, polymer resins, and composite materials such as fiberglass. The two rollers attached to the apparatus will usually have an uneven surface, or “teeth” (i.e. any uneven surface of any configuration, which includes ridges, striations, individual protrusions, etc.), and are driven mechanically. As such, one exemplary roller material is metal. The teeth on the surface of the roller can have several different arrangements, such as that the alignment of the teeth is parallel to the axis of the roller or forms an angle relative to the axis of roller. The teeth are usually evenly distributed on the surface of the roller for the consistency of the quality of the filament network produced. In contrast, the two rollers on the pendulum carrier preferably have “cots” (i.e., outside covering) and are slave rollers which are driven by the other two rollers attached to the apparatus. The cots can be made from various materials such as rubbers, plastics, polymers, natural polymers, cotton, ceramics, metals, and alloys. In one aspect, the cot is rubber with hardness of 50 to 90. In another aspect, the rubber cot has a hardness of 75.

Essentially, the drafting component stretches, breaks, and randomizes the long and organized precursor fibers to form a wool-like filament network. Drafting is accomplished by a stretching force created due to the difference in speed between pairs of rollers, wherein at least one downstream pair of rollers operates at a greater speed than the closest upstream pair of rollers. The pressure on the rollers is adjusted according to the type of feed fiber and the drafting ratio. The pressure on the rollers can be same or different. In the present invention, this is accomplished using different pendulum weights. By varying the speed difference and the pressure exerted by the pendulum, the apparatus is able to process different fibers with various tows, and produce filament networks with various characteristics, such as different average filament diameters.

In another embodiment, the drafting component has three or more pairs of rollers. In one aspect, the drafting component has no greater than 10 pairs of rollers. In another aspect, the drafting component has three to six pairs of rollers. In yet another aspect, the drafting component has three pairs of rollers. As depicted in FIG. 4, the arrangement of rollers is such that the fiber being drafted first contacts roller pair 3 (first rollers, then passes through the second rollers, and comes out of the last rollers as a stretched fiber for further drafting or as a fluffy filament network intermediate. The three pairs of rollers can have a variety of arrangements within the drafting component. One exemplary arrangement for the three pairs of rollers is illustrated in FIG. 4. Similar to other two pairs, the second rollers are so arranged that the center of each roller, the axis, is parallel to each other. Optionally, the axes of the second rollers may also be parallel to one of the other two pairs or both. Preferably, the drafting component has a pendulum carrier as a single weight element which cooperatively exerts appropriate pressure to all three pairs of rollers. Similar to the drafting component described above, one roller from each pair is attached to the pendulum carrier and the other roller is attached to the apparatus. However, the second rollers are removable from the apparatus so that the drafting component can easily be transformed into a drafting component with two pairs of rollers as described above and vice verse. The pressure exerted onto each pair of rollers is adjusted by the weight of pendulums and by varying the relative position of pendulums on the pendulum carrier to rollers. The three rollers attached to the apparatus are preferably metal rollers with teeth and driven mechanically whereas the other three are slave rollers and driven by its counterpart. The teeth on the surface of the roller can have several different arrangements. For example, the alignment of the teeth can be parallel to the axis of the roller or form an angle relative to the axis of roller. Preferably, the teeth are evenly distributed on the surface of the roller for the consistency of the quality of the filament network produced. On the other hand, the three rollers on the pendulum carrier preferably have cots. In one aspect, the cot is rubber with hardness of 50 to 90. In another aspect, the rubber cot has a hardness of 75.

Typically, the speed of the second rollers is driven slight faster than that of the first rollers so that a small force is exerted on the fiber. Often, this force is used to straighten the fiber for effective drafting. Sometimes, the incorporation of the second rollers also enhances the stability of the drafting component for sustainable and continuous operation. Drafting is accomplished by a stretching force created due to the difference in speed between the last and immediately upstream pairs of rollers. The second rollers run slower than the last pair under appropriate pressure to prevent slipping. However, the draft ratio is calculated based on the ratio of the speed of the last rollers verse the speed of the first rollers. The pressure on each pair of rollers can be adjusted according to the type of feeding fiber and the drafting ratio. In the present invention, this is accomplished using different weight of pendulums and relative position of pendulums to the rollers. By varying the speed difference and the pressure exerted by the pendulum, the apparatus is able to process different fibers with various tows as well as two or more fibers, of the same kinds or different types, simultaneously.

In another aspect of the present invention, the apparatus further comprises a spinning component as depicted in FIG. 2. By incorporating this third component, the filament network is directly processed into fine yarn with a yarn count of 1 to 60 Nm on the same apparatus. In one aspect, the oxidized PAN filament networks drafted from small tow PAN of various tow sizes can be spun into yams with about 10 to 28 Nm. The unit, “Nm”, is a measure of the thickness of yarn in term of the length in meters for one gram of yam. For instance, if one gram of yarn is 20 meters in length, then the yarn count is 20 Nm. Therefore, the higher the Nm, the thinner the yams. The process of the present invention can produce very thin yarn in a simple, efficient and economical process.

Intermediate

The apparatus of the present invention can process a variety of different fibers as disclosed above and produce a wool-like filament network intermediate with distinct physical characteristics from the precursor fiber. Unlike the well organized and aligned filaments of a precursor fiber, the filament network produced using the present invention is a wool-like collection of random filaments with very little parallel interactions between individual filaments and no visible twist between the individual filaments. The filament network may be composed of filaments from a single fiber. The intermediate may also be composed of filaments from several fibers to form blended filament networks. The blended networks may be formed by drafting two or more different fibers on the same apparatus simultaneously or by mixing the intermediate networks obtained individually. These filament network intermediates can be further processed into yams with very small yarn count and with additional enhanced properties and characteristics, such as increased tensile strength.

Generally, an individual filament of the network intermediate has a diameter of no greater than that of the original filament of the precursor fiber, and the intermediate contains multiple short wavy filaments that are randomly piled together. In one embodiment, the filament networks were obtained from an aligned and continuous oxidized PAN fiber with filaments of no greater than 192K. Preferably, the precursor fiber has filaments of no greater than 96K. More preferably, the precursor fiber has filaments of no greater than 48K. Yet more preferably, the precursor fiber has filaments of no greater than 24K. Yet more preferably, the precursor fiber has filaments of no greater than 12K. Each filament of the oxidized PAN network thus produce is no longer than 40 cm in length.

In another embodiment, the fluffy filament network was obtained from an aligned and continuous stainless steel fiber with filaments of no greater than 192K. Preferably, the precursor fiber has filaments of no greater than 96K. More preferably, the precursor fiber has filaments of no greater than 48K. Yet more preferably, the precursor fiber has filaments of no greater than 24K. Yet more preferably, the precursor fiber has filaments of no greater than 12K. Each filament of stainless steel network has a length of no greater than 40 cm.

In yet another embodiment, the fluffy filament network was obtained from an aligned and continuous aramid fiber with a tow of no greater than 192K. Preferably, the precursor fiber has filaments of no greater than 96K. More preferably, the precursor fiber has filaments of no greater than 48K. Yet more preferably, the precursor fiber has filaments of no greater than 24K. Yet more preferably, the precursor fiber has filaments of no greater than 12K. Each filament of aramid network has a length of no greater than 40 cm.

Post-Processing

The filament networks produced using the present invention can be further processed mechanically and/or chemically. The filament networks may be used in substantially any desired fabricated form, woven or non-woven. The networks can be readily spun into yarn using conventional processes. The fibers can then be woven, stitched, braided, knitted, or formed into non-woven sheets, as well as other flat or three-dimensional shaped structures. Exemplary products obtained through mechanical processing are herringbone weave cloth, twill weave tape, tubular woven fabric, paper, blankets, roving, yarn, cord, and rope. Filamentous materials can also be formed directly into sheets and other structures, either alone or in combination with other filaments, fibers, or compositions, such as resin.

The filament networks may also be treated chemically to impart new characteristics. For example, the filament networks may be fluorinated as disclosed in U.S. Pat. No. 4,857,394 so as to provide flexible fibers with different electrical conductivity. Another example is to convert oxidized PAN filament networks into carbon fibers by pyrolysis. This process involves two steps: carbonization and graphitization. During the carbonization process, the filament network is treated at about 1,000° C. in an inert atmosphere to further remove the non-carbon elements to yield carbon fiber with a carbon content of over 90%. During graphitization, the fiber is further treated at temperatures between 1,500-3,000° C. to improve the ordering and orientation of the crystallites in the direction of the fiber axis.

Applications

The filament networks produced by the process of the present invention can be used as intermediates for the production of a range of industrial and consumer products. For example, oxidized PAN filaments are chemically resistant, thermally stable, and physiologically harmless. The filament networks also have excellent processing properties such as superior blending and handing characteristics. They are ideally suited for heat resistant, thermal and acoustic insulation and technical textiles. The oxidized PAN filament networks can also be used as asbestos replacing additives in friction linings of automotive disc and drum brakes.

The oxidized PAN filaments and their downstream products such as yams and fabrics can be further processed under high temperatures into carbon fibers that have very high flame proof characteristics and are electrically conductive. Such carbon-based intermediate materials are useful in the production of a variety of industrial and consumer products, such as apparel and other textile-based products, belts and hoses, composites, fiber optics, electromechanical materials, friction sensitive products such as gaskets and brake pads, tires, ropes and cables. The filament networks can also be processed into activated PAN fiber. This product has very high surface area thus has high adsorption rate and capacity. It can be used to develop air filter, mask, water purification, odor adsorbing cloth, and protecting clothing.

EXAMPLES

The apparatus for the following examples had either two or three pairs of rollers as indicated in each example. All of the rollers attached to the apparatus had the same diameter of 31.84 mm, whereas all of the rollers attached to the pendulum had cots with the same hardness, i.e., 75.

Example I An Oxidized PAN Filament Network Produced from a Fiber with a Tow of 6K

The precursor fiber is an oxidized PAN with a tow size of 6K, a tow denier of 7,200, and tow weight of 0.8 g/meter. Its general physical properties are summarized in Table 1. The precursor fiber contains parallel filaments of a uniform length equal to the length of tow, which often exceeds 2 meters. The filament is also well organized and aligned longitudinally. Additionally, the precursor fiber has very limited twists, typically less than 5 turns per meter. The oxidized PAN fiber was drafted using the apparatus with two pairs of rollers, the first rollers and last rollers. The distance between two rollers attached to the apparatus was set to about 240 mm. To obtain a draft ratio of 27.2, the speeds of the last and preceding rollers were set at 227 and 8.3 rpm, respectively. The same pressure was applied to both pairs of rollers. The pressure was adjusted to about 28 Kg by varying the weight on the pendulum carrier. The drafting process broke and randomized the long and organized filaments of the precursor fiber to form a fluffy web which has very little parallel interactions between individual filaments and no visible twist between the individual filaments. The filament of the network appears wavy and has a length of no greater than about 22 cm and a width of no greater than 12 micrometers. The network has an average weight of about 0.077 g/10cm. TABLE 1 Physical Properties Data Filament denier 1.2 denier Density 1.40 g/cm³ Single filament diameter 11 micrometer Tensile strength 2.0 g/denier Elastic modulus 450 Kg/mm² Moisture regain  9% Strength at break 14 CN/tex Elongation at break 10% LOI 55 

The filament network was further processed by winding and twisting to yield a yarn with a yarn count of 34 Nm, a tensile strength of 250-300 g, a tensile elongation of 10%, and a twist count of 525 (T/meter).

Example II An Oxidized PAN Filament Network Produced from a Fiber with a Tow of 12K

The precursor fiber is an oxidized PAN with a tow size of 12K, a tow denier of 14,400, and tow weight of 1.6 g/meter. Its general physical properties are summarized in Table 1. The precursor fiber contains parallel filaments of a uniform length equal to the length of tow, which often exceeds 2 meters. Additionally, the precursor fiber has very limited twists, typically less than 5 turns per meter. The oxidized PAN fiber was drafted using the apparatus having only first and last pairs of rollers. The distance between the rollers attached to the apparatus was set to about 240 mm. To obtain a draft ratio of 8, the speeds of the first and last rollers were set at 125 and 15.6 rpm, respectively. The pressures applied onto the first and last rollers were 42 and 45 Kg, respectively. The pressure was adjusted by varying the weight on the pendulum carrier and the position of the pendulum on the pendulum carrier. The drafting process broke and randomized the long and organized filaments of the precursor fiber to form a wool-like filament network, which has very little parallel interactions between individual filaments and has no visible twists between individual filaments. The filaments of the network appear wavy and have a length of no greater than about 22 cm and a width of no greater than about 12 micrometers. The network has an average weight of about 0.159 g/10 cm.

The filament network was further processed by winding and twisting to yield a yarn with a yarn count of 5 Nm, a tensile strength of about 2000 g, a tensile elongation of 10%, and a twist count of 100 (T/meter).

Example III An Oxidized PAN Filament Network Produced from Two Feeding Fibers

This example illustrates the drafting of two fibers of the same type simultaneously. However, the drafting process is equitably applicable to two or more fibers of different kinds. The two fibers were fed using a feeding component as depicted in FIG. 1. The two precursor fibers are oxidized PAN fibers with a tow size of 6K, a tow denier of 7,200, and tow weight of 0.8 g/meter. Their general physical properties are summarized in Table 1. The precursor fiber contains parallel filaments of a uniform length equal to the length of tow, which often exceeds 2 meters. The filament is also well organized and aligned longitudinally. Additionally, the precursor fiber has very limited twists, typically less than 5 turns per meter. The oxidized PAN fibers were drafted using the apparatus with two pairs of rollers. The distance between the two rollers attached to the apparatus was set to about 240 mm. To obtain a draft ratio of 27.2, the speeds of the rollers were set at 227 and 8.3 rpm, respectively. The same pressure was applied to both sets of rollers. The pressure was adjusted to about 28 Kg by varying the weight of a pendulum on the pendulum carrier. The drafting process broke and randomized the long and organized filaments of the precursor fibers to produce a wool-like filament network which has very little parallel interactions between individual filaments and has no visible twist between the individual filaments. The filament of the network appears wavy and has a length of about no greater than about 22 cm and a width of no greater than about 12 micrometers. The network has average weight of about 0.154 g/10 cm.

The filament network was further processed by winding and twisting to yield a yarn with a yarn count of 17 Nm, a tensile strength of about 500-600 g, a tensile elongation of about 10%, and a twist count of about 375 (T/meter).

Example IV A Stainless Steel Filament Network

The precursor fiber is a stainless steel fiber with a tow size of 4K, and tow weight of 1.6 g/meter. In addition to its major chemical element, iron (Fe), the steel fiber also contains several other elements as listed in Table 2. The precursor fiber contains parallel filaments of a uniform length equal to the length of tow, which often exceeds 2 meters. The filament is also well organized and aligned longitudinally. Additionally, the precursor fiber has very limited twists, typically less than 5 turns per meter. The filament has a tenacity strength of 7.5 CN and a diameter of 8 micrometer. The stainless steel fiber was drafted using the apparatus with three pairs of rollers. The distance between the first and second rollers attached to the apparatus was set to be 100 mm whereas the distance between the second and the third rollers attached to the apparatus was set to be 140 mm. To obtain a draft ratio of 17.6, the speeds of the first, second and third rollers were set at 200, 11.4, and 10.8 rpm, respectively. The same pressure was applied to the first and second rollers and was set at 42 Kg. The pressure applied onto the first rollers was set at 45 Kg. Similar to the previous examples, the pressure was adjusted by varying the weight of the pendulum and the position of the pendulum on the pendulum carrier. The drafting process broke and randomized the long and organized filaments of the precursor fiber to form a wool-like filament network which has very little parallel interactions between individual filaments and has no visible twist between the individual filaments. The filament of the network appears wavy and has a length of no greater than about 10 cm and a width of about 8 micrometers. The network has an average weight of about 0.16 g/10cm. TABLE 2 Chemical Compositions Percent (%) C 0.03 Si 1.0 Mn 2.0 Ni 10.0-14.0 Cr 16.0-18.0

The filament network was further processed by winding and twisting to yield a yarn with a yarn count of 11 Nm and a twist count of 500 (T/meter).

Example V

An Aramid Filament Network Produced from an Aramid Fiber with a tow of 1K

The precursor fiber is an aramid fiber with a tow size of 1K, a tow denier of 1,530, and tow weight of 0.17 g/meter. Its general physical properties are summarized in Table 3. The precursor fiber contains parallel filaments of a uniform length equal to the length of tow, which often exceeds 2 meters. The filament is also well organized and aligned longitudinally and has a diameter of 12 micrometer. Additionally, the precursor fiber has very limited twists, typically less than 5 turns per meter. The aramid fiber was drafted using the apparatus with two sets of rollers, the first and last rollers. The distance between the first and last rollers mounted on the apparatus was about 240 mm. To obtain a draft ratio of 8.5, the speeds of the first and last rollers were set at 170 and 10 rpm, respectively. The pressures applied onto the first and last rollers were above about 42 and 45 Kg, respectively. The pressure was adjusted by varying the weight of the pendulum and the position on the pendulum carrier. The precursor aramid fiber was drafted twice. The first drafting resulted in a stretched fiber. The second drafting broke and randomized the long and organized filaments of the precursor fiber to form a wool-like filament network which has very little parallel interactions between individual filaments and has no visible twist between the individual filaments. The filament of the network appears wavy and has a length of no greater than about 22 cm and a width of about 12 micrometers. The network has an average weight of about 0.015 g/10 cm. TABLE 3 Physical Properties Data Filament denier 1.53 denier Tenacity 23 g/denier Tensile strength 3,000 N/mm² Tensile modulus 67 kN/mm² Elongation at break   3% Filament diameter 12 micrometer Density 1.38 g/cm³ Decomposition point 500 LOI  29

The filament network was further processed by winding and twisting to produce a yarn with a yarn count of 50 Nm and a twist count of 800 T/meter.

The examples set forth above are provided to give those of ordinary skill in the art with a complete disclosure and description of how to make and use the preferred embodiments of the compositions, and are not intended to limit the scope of what the inventors regard as their invention. Modifications of the above-described modes (for carrying out the invention that are obvious to persons of skill in the art are intended to be within the scope of the following claims. All publications, patents, and patent applications cited in this specification are incorporated herein by reference as if each such publication, patent or patent application were specifically and individually indicated to he incorporated herein by reference. 

1. A method for producing a filament network comprising the steps of: a) providing at least one starting fiber comprising a plurality of longitudinally aligned filaments; b) introducing the starting fibers into a drafting component, wherein the drafting component comprises a first pair of rollers and a second pair of rollers, wherein the second pair of rollers is downstream of the first pair, and wherein the first pair of rollers turns at a first speed and the second pair of rollers turns at a second speed; c) drawing the starting fibers through the drafting component between the first pair of rollers and the second pair of rollers while applying pressure onto the first pair of rollers and the second pair of rollers, wherein the second speed is faster than the first speed, to form a filament network comprising a wool-like random collection of wavy filaments.
 2. The method of claim 1, wherein the second speed is between 1.1 to 50 times faster than the first speed.
 3. The method of claim 1, wherein step a) further comprises providing two precursor fibers.
 4. The method of claim 1, wherein at least one precursor fiber is a stainless steel fiber.
 5. The method of claim 1, wherein at least one precursor fiber is a polymeric material.
 6. The method of claim 5, wherein the polymeric material is an aramid fiber.
 7. The method of claim 5, wherein the polymeric material is oxidized PAN.
 8. The method of claim 7, wherein the precursor fiber has filaments of no greater than 192K.
 9. The method of claim 7, wherein the precursor fiber has filaments of no greater than 96K.
 10. The method of claim 7, wherein the precursor fiber has filaments of no greater than 48K.
 11. The method of claim 1 further comprising the step of forming yarn from the filament network.
 12. An apparatus for drafting at least one precursor fiber comprising a plurality of longitudinally aligned filaments to form a fibrous network, wherein said apparatus comprises: a) a first pair of rollers having a first rolling speed; b) a second pair of rollers downstream from the first set of rollers having a second roller speed, wherein the second roller speed is at least 1.1 times greater than the first speed; and c) a pressurizing element that applies pressure onto both the first and second pairs of rollers.
 13. The apparatus of claim 12, wherein the pressurizing element is a weighted element that applies pressure cooperatively onto both the first and second pair of rollers.
 14. The apparatus of claim 13, wherein the weighted element is a pendulum carrier.
 15. The apparatus of claim 12, wherein one roller in the first and second pairs of rollers is a metal roller with teeth.
 16. The apparatus of claim 12, wherein one roller in the first and second pairs of rollers has a cot with a hardness of about 75 to
 90. 17. The apparatus of claim 12 further comprising an intermediate pair of rollers between the first and second pairs of rollers, and driven at an intermediate speed faster than the first speed.
 18. The apparatus of claim 17, wherein the intermediate speed is between 1.1 to 50 times faster than the first speed.
 19. A filament network made from a fibrous starting material, wherein the fibrous starting material further comprises a plurality of aligned individual filaments with limited twists, and wherein said filament network comprises a plurality of filaments held together by mechanical, physical and noncovalent chemical forces.
 20. The network of claim 19, wherein said fibrous starting material is fibers of the same type.
 21. The network of claim 20, wherein the fiber is a stainless steel fiber having no greater than 192K filaments.
 22. The network of claim 21, wherein each filament of the network made from the stainless fiber has a length of no greater than 40 cm.
 23. The network of claim 20, wherein the fiber is a polymeric fiber having no greater than 192K filaments.
 24. The network of claim 23, wherein each filament of the network made from the polymeric fiber has a length of no greater than 40 cm.
 25. The network of claim 23, wherein the polymeric fiber is an aramid fiber.
 26. The network of claim 23, wherein the polymeric fiber is oxidized polyacrylonitrile (PAN).
 27. The network of claim 26, wherein the oxidized PAN has a density of between 1.30 to 1.50 g/cm³, a carbon content of between 55 to 68%, and a Limiting Oxygen Index (LOI) value of between 40 to 60%.
 28. The network of claim 26, wherein the oxidized PAN fiber has no greater than 96K filaments of no greater than 25 micrometers in diameter in each filament.
 29. The network of claim 26, wherein each filament of the network made from the oxidized PAN fibers has a length of no greater than 40 cm, a diameter of no greater than 20 micrometers, and an average weight of no greater than 0.4 g/10 cm. 